1. Field of the Invention
The invention relates to an x-ray device provided with an X-ray source and an X-ray detector which are mounted at a respective end of a common holding device, the holding device being connected to the room by way of a supporting device, wherein the supporting device is composed of a plurality of hinged, serially interconnected supporting members.
2. Description of the Related Art
Furthermore, WO 99/30614 discloses a C-arm X-ray device in which the supporting device is constructed as a parallel manipulator. Therein, a first holding plate that is attached to the C-arm is connected to a second holding plate via a plurality of supporting members; the second holding plate can be attached, for example, to the wall. Each of said supporting members; is connected directly to both holding plates, the points of connection of the supporting members to the holding plates being different. The C-arm can thus be moved to given positions within given limits.
U.S. Pat. No. 4,894,855 discloses an X-ray device in which the X-ray tube, the X-ray detector and the patient table are mounted on a respective manipulator which consists of a plurality of supporting members, thus enabling a motion of these elements in all three spatial directions that is independent of one another.
It has been found that the solution known from WO 99/30614 has the drawback that the flexibility and the possibilities for movement are limited notably because of the mechanical construction. For many applications, for example for 3D rotation angiography, however, it is necessary to form X-ray images from a large variety of positions, that is, that for example a series of X-ray projection images can be formed along a predetermined trajectory. This should also take place with an as high as possible positioning accuracy. Granted, the X-ray device known from U.S. Pat. No. 4,894,855 offers a high flexibility, but the accuracy that can be achieved thereby is not adequate for many applications. Moreover, it requires a plurality of manipulators, each of which must be separately controlled; this leads to high costs and necessitates complex control.
Therefore, it is an object of the invention to provide an as flexible as possible X-ray device which offers a high positioning accuracy and can be manufactured as economically as possible.
This object is achieved by means of an X-ray device as disclosed in claim 1.
The invention is based on the recognition of the fact that neither a rigid supporting device nor a supporting device in the form of a parallel manipulator constitutes the optimum solution with respect to flexibility. Therefore, the supporting device according to the invention is composed of a plurality of hinged, serially interconnected supporting members which are preferably also individually controllable so that the holding device can be moved in all spatial directions. The necessary positioning accuracy is also achieved in that the holding device is preferably constructed so as to be rigid, so that the distance between the X-ray tube and the X-ray detector and the orientation of these elements relative to one another are invariable. Moreover, in this case only the supporting device is composed of a plurality of supporting members that must be controlled, whereas the X-ray device that is known from U.S. Pat. No. 4,894,855 includes a plurality of manipulators that must be separately controlled.
The supporting device in a preferred embodiment of the invention is a serial manipulator, notably a robot arm. Use can be made notably of a serial robot arm as is known from many manufacturing technical fields. This may lead to a reduction of costs, because the numbers in which C-arm X-ray devices are manufactured are very small, so that the cost of manufacturing the mechanical systems constitutes a significant cost factor. The use of a conventional robot arm that is manufactured in large numbers, however, enables the cost of this part of the mechanical system to be reduced to some extent while the freedom of movement is increased at the same time. Such robot arms can be simply controlled by means of known and standardized software. Because robot arms of this kind also operate at a high speed, the period of time required for the formation of X-ray images could also be reduced. For example, a real-time study of the blood flow could be possible.
The supporting device in a preferred further embodiment is constructed in such a manner that the X-ray source and the X-ray detector can be positioned completely as desired and/or the motions of the individual supporting members of the supporting device are controllable. In order to enable the X-ray tube to follow circular or helical trajectories as required in rotation angiography, the supporting device in a further preferred embodiment yet is connected to the holding device by way of a hinge.
Even though the holding device is preferably constructed as a rigid C-arm, the holding device may alternatively be composed of at least two holding members, the X-ray source being mounted on a first holding member whereas the X-ray detector is mounted on the second holding member. This offers the advantage that the distance between the X-ray source and the X-ray detector can also be changed, so that the imaging scale and the size of the examination zone can be varied and the overall flexibility is further enhanced.
Conventional robot systems usually have a mechanical emergency braking system for stopping the motion of the robot in the case of a failure or incorrect control. Because injury of a patient must be avoided at all costs in medical applications, a preferred embodiment is provided with means for monitoring the distance between an object to be examined and moving parts of the X-ray device, notably the X-ray source and the X-ray detector; for example, ultrasound sensors and ultrasound detectors can be used for this purpose. They continuously measure the distance between the moving parts and the object to be examined and initiate emergency braking as soon as the distance becomes too small and a risk of injury of the object to be examined arises. The distance initiating such an emergency braking operation, however, should be adjusted in such a manner that on the one hand all necessary X-ray images can still be formed while on the other hand emergency braking is still possible within the distance remaining before contact occurs.
Further feasible means for monitoring the distance consist of mechanical contact sensors mounted on the X-ray source and the X-ray detector, for example feeler-like sensors in the form of long bristles which produce a sensor signal upon contact with the object to be examined, so that emergency braking can be initiated. Another feasible means for monitoring is a separate video system which continuously monitors the motion of the X-ray source and the X-ray detector in real time so as to evaluate this motion and initiate emergency braking when the distance becomes too small.